This invention relates to a rotary heating blow-molding machine for fabricating a bottle-shaped container of biaxially oriented synthetic resin such as plastic and, more particularly, to a blow-molding machine for fabricating a thin-walled transparent high-impact plastic container of high molding accuracy by orientation-blowing synthetic resin such as polyethylene terephthalate.
In an ordinary process for molding a blow-molded bottle-shaped container of biaxially oriented synthetic resin, there is generally adopted a process for blow-molding the container by the steps of extrusion-molding a cylindrical preformed piece or parison in an extrusion molding machine, engaging the parison thus extrusion-molded in split blowing molds and cutting it in predetermined length, and blowing compressed fluid (generally air) into the parison thus engaged to thereby expand the parison thus engaged in the split molds so as to thus blow-mold a bottle-shaped container.
In such a process, however, the parison thus blow-molded into a bottle-shaped container is only radially oriented uniaxially, but is not oriented in the axial direction at all.
An injection blow molding process is utilized to eliminate the disadvantages of the above described extrusion blow molding process.
This injection blow molding process blow-molds a bottle-shaped container by the steps of orienting a preformed piece of cylindrical shape with a bottom preformed by an injection molding machine or by an extrusion molding machine in a blowing mold and introducing compressed fluid or air into the blow mold to thereby radially orient the piece. According to the injection blow molding process, since the molded product is biaxially oriented, it can be sufficiently oriented to improve various mechanical properties such as durability and mechanical strength and transparency.
In case where the preformed piece is molded by an injection molding process, the degree of the viscosity of synthetic resin material used for the preformed piece does not become a problem. Since the process can, however, employ synthetic resin having good moldability and low viscosity such as, for example, saturated polyester resin, it can freely select and use synthetic resin material having adequate physical properties for the intended purpose as a bottle.
The most general example of carrying out the injection blow molding process installs separately an injection molding machine and a blow-molding machine and thus fabricates a blow-molded product by the steps of conveying a preformed piece molded in the injection molding machine into the blow-molding machine, uniformly heating the preformed piece cooled at separating and conveying time from the injection molding machine to the temperature capable of biaxially orienting it before setting it in the blow-molding machine, and then setting the piece thus uniformly heated in the blow-molding machine to thereby blow-mold the piece into the final product.
There are various types of a heating blow-molding machine having the blow-molding machine and a heating unit in combination. The typical fundamental constitution of such a heating blow-molding machine incorporates a heating unit and a blow-molding machine of turntable construction and fabricates a product by the steps of uniformly heating numerous preformed pieces while rotating the pieces around a center thereof, sequentially feeding the pieces thus heated to a blow-molding machine, engaging the pieces thus heated one by one with numerous blowing molds rotating around a center as attached to a turntable in the blow-molding machine, and orientating blow-molding the pieces thus engaged and discharging the pieces.
The operations of feeding the pieces to the blow-molding machine and conveying the pieces or final products between the turntables are automatically controlled at a set time period upon stoppage of the respective turntables by intermittently turning the turntables of the heating unit and blow-molding machine at every predetermined interval of central angle.
Since the turntables are thus intermittently rotated, this heating blow-molding machine can easily take a timing for feeding the pieces and the final products betwen the turntables to thus easily center the pieces and the products in the conveyance, however since the pieces and the products are thus intermittently fed, the heating blow-molding machine can fabricate fewer pieces and products per unit time, namely less productivity with bulky, complicated and expensive facilities. Further, the intermittent rotation and operation of the heating blow-molding machine vigorously wears the respective portions, particularly bearings and braking units, and results in a great deal of vibration, thus causing serious disadvantages.